Fix go-ipfs#7242: Remove "HEAD" from Allow methods

(when GET is not allowed).

http/errors_test.go

@@ -165,7 +165,7 @@ func TestUnhandledMethod(t *testing.T) {
 		AllowGet: false,
 		Code:     http.StatusMethodNotAllowed,
 		ResHeaders: map[string]string{
-			"Allow": "POST, HEAD, OPTIONS",
+			"Allow": "POST, OPTIONS",
 		},
 	}
 	tc.test(t)

http/handler.go

@@ -192,10 +192,10 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 }
 
 func setAllowedHeaders(w http.ResponseWriter, allowGet bool) {
-	w.Header().Add("Allow", http.MethodHead)
 	w.Header().Add("Allow", http.MethodOptions)
 	w.Header().Add("Allow", http.MethodPost)
 	if allowGet {
+		w.Header().Add("Allow", http.MethodHead)
 		w.Header().Add("Allow", http.MethodGet)
 	}
 }